Anticholinergic

An anticholinergic agent is a member of a class of pharmaceutical compounds (such as Dicyclomine) which serve to reduce the effects mediated by acetylcholine in the central nervous system and peripheral nervous system.

Anticholinergics are typically reversible competitive inhibitors of one of the two types of acetylcholine receptors, and are classified according to the receptors that are affected:

• antimuscarinic agents operate on the muscarinic acetylcholine receptors. (The majority of anticholinergics are antimuscarinics.)
• antinicotinic agents operate on the nicotinic acetylcholine receptors.

When a significant amount of anticholinergic is taken into the body, a toxidrome known as acute anticholinergic syndrome may result. This may happen accidentally or intentionally as a form of recreational drug use. This class of drug is usually considered the least “fun” by experienced drug users, possibly due to the lack of euphoria caused by anticholinergics. Because most users do not enjoy the experience, they do not use it again, or very rarely. Risk of addiction is low in the anticholinergic class. Effects are usually more pronounced in the elderly, due to the decrease of acetylcholine production associated with age.

Possible effects of anticholinergics include:

• Ataxia; loss of coordination
• Decreased mucus production in the nose and throat; consequent dry, sore throat
• Xerostomia or dry mouth
• Cessation of perspiration; consequent increased thermal dissipation through the skin leading to hot, red skin
• Increased body temperature
• Pupil dilation (mydriasis); consequent sensitivity to bright light (photophobia)
• Loss of accommodation (loss of focusing ability, blurred vision — cycloplegia)
• Double vision (diplopia)
• Increased heart rate (tachycardia)
• Urinary retention
• Diminished bowel movement, sometimes ileus
• Increased intraocular pressure, dangerous for people with narrow-angle glaucoma
• Shaking

Possible effects in the central nervous system resemble those associated with delirium, and may include:

• Confusion
• Disorientation
• Agitation
• Respiratory depression
• Short-term memory loss
• Inability to concentrate
• Wandering thoughts; inability to sustain a train of thought
• Incoherent speech
• Wakeful myoclonic jerking
• Unusual sensitivity to sudden sounds
• Illogical thinking
• Photophobia
• Visual disturbances
  • Periodic flashes of light
  • Periodic changes in visual field
  • Visual snow
  • Restricted or “tunnel vision”
• Visual, auditory, or other sensory hallucinations
  • Warping or waving of surfaces and edges
  • Textured surfaces
  • “Dancing” lines; “spiders”, insects
  • Lifelike objects indistinguishable from reality
• Rarely: seizures, coma and death

Acute anticholinergic syndrome is completely reversible and subsides once all of the toxin has been excreted. Ordinarily, no specific treatment is indicated. However, in extreme cases, especially those that involves severe distortions of mental state, a reversible cholinergic agent such as physostigmine may be used.

The most common plants containing anticholinergic alkaloids are:

• Atropa belladonna (Deadly Nightshade)
• Mandragora officinarum (Mandrake)
• Hyoscamus niger (Henbane)
• Datura species (Datura)

Some drugs, such as hydrocodone, are mixed with small amounts of an anticholinergic, such as Homatropine Methylbromide to discourage abuse.

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